The vast majority of the electricity generated in the United States. is produced at large, centralized power stations, and then transmitted over high voltage power lines to remote customers. Such power transmission lines often distribute electricity many hundreds of miles away from the point of generation. Even using relatively high voltage levels to reduce current levels, the resistive losses involved in power transmission in this country is substantial.
From a historical perspective, such centralized power generation makes sense, since throughout the first half of the twentieth century, virtually all of this power was provided by steam-based power plants. Such plants operate by burning fossil fuels, predominantly coal, to boil water and produce steam. This steam passes through and rotates a turbine, driving a generator to produce electricity. Steady increases in steam technology translated into improved efficiency (measured by the amount of electricity generated per unit of fuel consumed), resulting in steady declines in the cost to produce power. Economies of scale favored the construction of large centralized facilities. Smaller turbines were less efficient, and few alternative technologies were available.
Natural gas-fired turbines have become the second most prevalent form of fossil-fueled electric power generating technology. These systems use the heat from the combustion process to accelerate combustion products through and rotate a turbine. The spinning turbine drives a generator to produce electricity. Such simple-cycle gas turbines can be improved by capturing the waste heat from the turbine exhaust to create steam, which is used to drive a steam turbine and produce additional electrical power. Theses combined-cycle gas turbine systems (CCGT) are more efficient (40-50%) than simple-cycle systems (25-35%) and coal-fired steam turbine plants (30-40%).
However, by the end of the century, the capital costs associated with building large centralized electric power generating facilities, the significant cost of providing thousands of miles of electrical transmission lines to distribute the electricity to those areas requiring electricity, and the emergence of technologies capable of competing with the costs and efficiencies of the by now mature turbine technologies, have enabled distributed electrical power generation to become a reasonable alternative to centralized electrical power production. This advantage is particularly true in locations where increasing demands for electricity will require significant capital expenditures to provide new transmission lines to bring additional electrical power from remote locations. Transmission losses can also be substantially reduced by using a more distributed power generation system.
Co-generation can provide a further advantage to distributed power systems. In a centralized electric power generating plant, enormous amounts of thermal energy (in the form of steam having insufficient pressure to drive a turbine) are unused and wasted. In fact, centralized electric power generating plants often require expensive systems to condense the unusable steam back into water, to be reheated once again to form usable stream. In urban areas, it is common to provide heating facilities that burn fuel oil or natural gas to provide heat, but do not produce electrical energy. However, in a co-generation facility, combustion of a hydrocarbon fuel can produce electrical power, and the remaining “waste” heat can be used for heating and cooling buildings and other facilities, eliminating the need to construct separate facilities. The use of waste heat from a smaller co-generation facility significantly improves its overall efficiency, even if the cost or efficiency of the electrical generation system alone is not on par with that achievable in a centralized larger power plant.
The ability of distributed power systems to compete effectively with centralized electrical power production became particularly apparent during the electrical power crisis experienced in the Western U.S. in the early part of 2001. As electrical rates soared, several municipalities and businesses turned to distributed electrical power generation as an alternative to purchasing the substantially more expensive electrical power available from centralized generating facilities. The city of Tacoma, Wash., embarked on a temporary diesel generator project (referred to as a generator farm) to gain relief from the uncertain spot market prices for electricity. The city of Tacoma estimates that during the nine-month period when this program was in effect, city consumers saved over $25 million compared to purchasing an equivalent amount of electricity from the centralized electrical power market.
Other municipalities are also aggressively pursuing distributed power alternatives. The New York Power Authority is seeking to obtain regulator approval to install eleven gas turbines at six different sites in New York City boroughs and on Long Island. The collective capacity of the units is 444 MW, which would help the transmission-constrained city meet expected summer peaks in electric power consumption.
Even diesel-electric locomotives have been used in an effort to ensure affordable and reliable power supplies. Montana Rail Link has interconnected the electrical power produce by two locomotives to the electrical grid in Butte, Montana. Early results indicated that each locomotive could provide roughly 1.5 MW of power, but that the cost of electricity produced would likely be too high to represent a viable alternative power source.
Clearly, distributed production of electrical power is experiencing tremendous growth. Concerns have been raised, however, about some of the technologies being employed in such distributed power systems. Diesel generators in particular have received negative attention, because of the harmful air emissions they produce. It is estimated that even using the lowest emission diesel generators available and employing additional pollution control devices, each generator operated by the city of Tacoma produced about the same amount of emissions every twenty-four hours as would have been produced by a diesel truck driven 6,000 miles. While the electricity was produced at a lower cost to the city, the “cost” to the environment was significantly higher than would have resulted if the same amount of power had been produced at most modern centralized electric power generating facilities. Higher emissions might be acceptable during a crisis, but small diesel generators do not represent an acceptable long-term solution.
It would therefore be desirable to provide a distributed electrical power generating system that can provide electricity in a manner that is competitive with centralized electric power generating facilities, both in cost and in regard to environmental impact considerations. Where natural gas is available and is of sufficient quality, gas-fired turbines offer a reasonable means for providing distributed electrical power generation. Advances in gas turbine technology have enabled much higher efficiencies to be achieved by gas turbines than were possible only 15 years ago. Many new centralized electric power generating facilities are based on installing multiple gas turbines, and several utilities are planning to build distributed electric power generating facilities consisting of small numbers of natural gas turbines, strategically located in urban or industrial areas of high demand. Natural gas is relatively clean burning, and minimal environmental controls are required to manage emissions produced by the combustion of natural gas. The most significant drawback to gas turbine generators is the requirement that they burn natural gas (or similar fuel gases), which is now in high demand and experiencing increases in price that are expected to worsen.
Fuel cells are another technology just entering the distributed power market. Fuel cells have long been available in small sizes for aerospace applications and are becoming available in larger sizes at significantly lower costs. Fuel cells can be characterized by the electrolytes, operating temperature, type of fuel gas, and oxidants used. Depending on the fuel cell type, mobile ions (OH−, H+, O2−, or CO32−) pass thru a membrane or separating matrix to combine with the fuel to produce water or CO2, while electrons migrate across an external circuit, producing electricity. The chemical process that causes this current flow is exothermic, resulting in an emission stream with concomitant heat output that can be used in other processes. The gaseous fuel supplied to a fuel cell may include hydrogen, carbon monoxide, methane, and hydrocarbons. The fuel generally has restrictions on sulfur content (mainly H2S), particulate loading, ammonia, halogens (e.g., HCl), and other constituents typically found in fossil fuel. Proton exchange membrane (PEM) fuel cells have high input restrictions—the fuel gas needs to consist of pure hydrogen; these fuel cell generally have very low tolerance to carbon monoxide. High-temperature fuel cell systems, such as molten carbonate fuel cells (MCFC) or solid oxide fuel cells (SOFC), can accept syngas mixtures (i.e., mixtures of hydrogen and carbon monoxide) with additional methane and hydrocarbons. CO2 is generally a diluent in the fuel gas; however, it is required in small quantities in MCFCs. Oxygen needed in the electrochemical reactions of high temperature fuel cells is usually supplied in form of air, which may be dried, preheated, or oxygen-enriched. As fuel cell technologies mature, and these products reach the market in increasing quantities, they will offer an attractive means for distributed electrical power generation.
One of the most abundant and readily available fuels in the U.S. is coal, which cannot be used directly in either gas turbines or fuel cells. Furthermore, there exists a host of carbonaceous alternative fuels, such as chemical process wastes, industrial wastes, waste oils, marine diesel, and chlorinated hydrocarbons, all of which possess fuel value, but which also cannot be used directly in gas turbines or fuel cells. It would thus be desirable to provide a distributed electrical power generating system that can produce electricity, using fuels other than natural gas or diesel oil, to take advantage of the availability of such fuels.
Marine diesel is generally used on ships for co-generation of electricity and steam that is used for propulsion and on-board utilities and services. New developments in naval architecture are focused on designs that use a predominance of electrical power for all shipboard functions, with a reduction in overall emissions. In this application, modern fuel cells may play an important role. It would therefore be desirable to provide a method and apparatus capable of reforming carbonaceous fuels into a form usable by either a fuel cell or gas turbine, thus enabling distributed electrical power generating systems to use fuels other than natural gas or hydrogen, and to allow new forms of electrical power production in naval applications.
It has been recognized in the art that plasma torches can be employed to reform chemical substances into other compounds. Applications for plasma torches in the prior art have generally focused on the use of direct current (DC) arc plasma torches to process bulk solid wastes and to destroy toxic wastes. The emphasis has been on waste volume reduction and destruction efficiency. In contrast, inductively coupled plasma (ICP) torches have been used primarily in plasma spraying for surface preparation and in the production of special materials (metal oxides and carbides) in low volume.
There have been investigations into using ICP torches to provide the thermal energy required to drive chemical reactions. For example, commonly assigned U.S. Pat. No. 6,153,852 describes the use of ICP torches to produce commercially valuable materials such as carbon monoxide (CO) and synthesis gas (a mixture of hydrogen (H2) and CO). While disclosing how an ICP torch can be used to generate synthesis gas from carbonaceous materials, the above-noted patent does not teach or suggest using such synthesis gas for electrical power generation, or provide any guidance on how ICP torch production of synthesis gas can be most efficiently employed to generate electrical power. It would therefore be desirable to provide a method and apparatus enabling an ICP torch to be used to reform carbonaceous fuels not suitable for use in fuel cells or gas turbines, into a fuel that can readily be employed in such device to efficiently produce electrical power, and thus, to provide an environmentally acceptable and cost-effective competitive alternative to centrally generated electrical power.